The present invention relates to connections between and methods of connecting field windings and exciter or slip rings in dynamoelectric machines and particularly relates to current carrying connections between and methods of connecting field windings and bore connectors and bore connectors and exciter or slip rings.
The rotors of dynamoelectric machines conventionally typically comprise relatively large diameter cylindrical bodies containing field windings for producing magnetic flux which in turn produces stator current and voltage. These field windings are normally carried in a series of longitudinal slots along the outer circumference and extend the length of the rotor body. Rotation of the body particularly at speeds of 3600 rpm, for example, exerts high centrifugal forces on the windings which are retained in the rotor slots through the use of dovetail shaped wedges which also extend along the length of the rotor body. The manner in which the windings and rotor slots are shaped, insulated and cooled present formidable design problems, particularly for units designed for long term operation under variable load and environmental conditions. Because the windings extend axially beyond the rotor body and wedge ends and are subjected to the same rotational forces which tend to thrust the winding end turns in a radially outward direction, specially designed structure must be included to prevent such radial movement, as well as for making electrical connections between the exciter or slip rings, for example, and the windings.
As to the problem of preventing radial movement of the end turns, it is conventional to enclose the winding end turns within retaining rings attached to the rotor body ends by shrink fitting such rings around circumferential lips at the ends of the rotor body. Other means, such as locking keys and the like, are additionally included to maintain the retaining rings securely on the rotor so as to counteract the effects of thermal expansion on the retaining rings.
As to the manner in which electrical connections may be made between the windings and bore connectors, also known as the "bore copper" (insulated conductors embedded in the smaller diameter shafts that extend from opposite ends of the rotor body, and which are ultimately connected to the exciter/rectifier assembly), such field winding connections as found in the prior art are conventionally brazed leaves of copper of various configurations. These configurations have exhibited premature failures due to cyclic mechanical and electrical duty requirements, which require the connectors to have particular characteristics.
More particularly, in a current long-standing design affording electrical connection between a field winding and a bore conductor (see, for example, U.S. Pat. No. 5,358,432), a main terminal is inserted into a radial bore of the shaft. The main terminal has tapered threads at its radial inner end for engaging female tapered threads in the bore connector. Tolerances of the taper angle, thread pitch, the contacts along minimum major and minor threaded diameters and the need to torque the main terminal to a predetermined value render the installation of the main terminal to bore connector connection difficult as well as affording less than optimal conditions for good electrical connection. The opposite end of the main terminal includes a plurality of flexible leaves which are typically electrically connected to the field winding. Because of the pipe thread type securement between the main terminal and bore connector, the thin terminal leaves are necessarily formed and brazed together in the field. In that process, care must be taken not to melt the necessary thin copper leaves or to allow the brazing alloy to migrate into the flexible part of the terminal. Field brazing of the leaves to one another and to the field winding is time consuming and laborious. Should the leaves melt in the course of brazing or should braze alloy migrate to the flexible part of the terminal, the high rotational and thermal forces of the rotor will cause the flexible connection to prematurely fail causing unscheduled outages and generator down time.
The bore connector to exciter/slip ring connections are conventionally similarly formed with a tapered pipe thread at the end of a stud for threaded connection with the tapered female threads in a second aperture of the bore conductor. The stud forms the electrical connection between the bore connector and the exciter/slip rings. Similar installation and cyclic duty problems occur in this connection as in the previously-described electrical connection. Consequently, there is a need to provide an improved electrical connection between the field windings and the exciter/slip ring connections which can be bench assembled with a precise configuration and braze solidification and can be inspected prior to assembly to the generator in the field and which eliminates the above-described threaded connections between the bore connector and the main terminal and stud as well as eliminate the torquing requirements.